The heat generating temperature dependent resistor formed of a heat generating portion and a non-heat generating portion supporting the heat generating portion such as wound type, thin film type and thick film type temperature dependent resistors used in the hot wire type air flow meter has two kinds of thermal inertias; one kind of a primary thermal inertia defined by the heat generating portion and causing a first stage delay in air flow rate signals, and the other kind is a secondary thermal inertia defined by the non-heat generating portion and further causing second stage delay in the air flow rate signals in response to flow rate changes during an operation of the hot wire type air flow meter.
The fuel amount of an automotive internal combustion engine is controlled in accordance with detected air flow rate signals from the air flow meter such that delayed or incorrect air flow rate signals during the air flow rate changes cause an improper fuel control for the automotive internal combustion engine.
Since the second stage delay in detected air flow rate signals caused by the thermal inertia of the non-heat generating portion of the hot wire resistor is substantial, and hitherto, many attempts have been made to reduce the thermal inertia of the non-heat generating portion in order to minimize the second stage delay in the air flow rate signals caused during air flow rate changes, for example, as disclosed in U.S. Pat. No. 4,715,224 issued on Dec. 29, 1987. However such attempts caused structural and manufacturing limitations of the hot wire resistors having a non-heat generating portion.